Add scripting (tengo) support for every incoming message (#731)

TengoModifyMessage allows you to specify the location of a tengo (https://github.com/d5/tengo/) script.
This script will receive every incoming message and can be used to modify the Username and the Text of that message.
The script will have the following global variables:
to modify: msgUsername and msgText
to read: msgChannel and msgAccount

The script is reloaded on every message, so you can modify the script on the fly.

Example script can be found in https://github.com/42wim/matterbridge/tree/master/gateway/bench.tengo
and https://github.com/42wim/matterbridge/tree/master/contrib/example.tengo

The example below will check if the text contains blah and if so, it'll replace the text and the username of that message.
text := import("text")
if text.re_match("blah",msgText) {
    msgText="replaced by this"
    msgUsername="fakeuser"
}

More information about tengo on: https://github.com/d5/tengo/blob/master/docs/tutorial.md and
https://github.com/d5/tengo/blob/master/docs/stdlib.md

42 files changed, 2862 insertions, 0 deletions

diff --git a/vendor/github.com/d5/tengo/objects/array.go b/vendor/github.com/d5/tengo/objects/array.go
new file mode 100644
index 00000000..1e917c59
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/array.go
@@ -0,0 +1,130 @@
+package objects
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/d5/tengo/compiler/token"
+)
+
+// Array represents an array of objects.
+type Array struct {
+	Value []Object
+}
+
+// TypeName returns the name of the type.
+func (o *Array) TypeName() string {
+	return "array"
+}
+
+func (o *Array) String() string {
+	var elements []string
+	for _, e := range o.Value {
+		elements = append(elements, e.String())
+	}
+
+	return fmt.Sprintf("[%s]", strings.Join(elements, ", "))
+}
+
+// BinaryOp returns another object that is the result of
+// a given binary operator and a right-hand side object.
+func (o *Array) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	if rhs, ok := rhs.(*Array); ok {
+		switch op {
+		case token.Add:
+			if len(rhs.Value) == 0 {
+				return o, nil
+			}
+			return &Array{Value: append(o.Value, rhs.Value...)}, nil
+		}
+	}
+
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *Array) Copy() Object {
+	var c []Object
+	for _, elem := range o.Value {
+		c = append(c, elem.Copy())
+	}
+
+	return &Array{Value: c}
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *Array) IsFalsy() bool {
+	return len(o.Value) == 0
+}
+
+// Equals returns true if the value of the type
+// is equal to the value of another object.
+func (o *Array) Equals(x Object) bool {
+	var xVal []Object
+	switch x := x.(type) {
+	case *Array:
+		xVal = x.Value
+	case *ImmutableArray:
+		xVal = x.Value
+	default:
+		return false
+	}
+
+	if len(o.Value) != len(xVal) {
+		return false
+	}
+
+	for i, e := range o.Value {
+		if !e.Equals(xVal[i]) {
+			return false
+		}
+	}
+
+	return true
+}
+
+// IndexGet returns an element at a given index.
+func (o *Array) IndexGet(index Object) (res Object, err error) {
+	intIdx, ok := index.(*Int)
+	if !ok {
+		err = ErrInvalidIndexType
+		return
+	}
+
+	idxVal := int(intIdx.Value)
+
+	if idxVal < 0 || idxVal >= len(o.Value) {
+		res = UndefinedValue
+		return
+	}
+
+	res = o.Value[idxVal]
+
+	return
+}
+
+// IndexSet sets an element at a given index.
+func (o *Array) IndexSet(index, value Object) (err error) {
+	intIdx, ok := ToInt(index)
+	if !ok {
+		err = ErrInvalidIndexType
+		return
+	}
+
+	if intIdx < 0 || intIdx >= len(o.Value) {
+		err = ErrIndexOutOfBounds
+		return
+	}
+
+	o.Value[intIdx] = value
+
+	return nil
+}
+
+// Iterate creates an array iterator.
+func (o *Array) Iterate() Iterator {
+	return &ArrayIterator{
+		v: o.Value,
+		l: len(o.Value),
+	}
+}
diff --git a/vendor/github.com/d5/tengo/objects/array_iterator.go b/vendor/github.com/d5/tengo/objects/array_iterator.go
new file mode 100644
index 00000000..204faa41
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/array_iterator.go
@@ -0,0 +1,57 @@
+package objects
+
+import "github.com/d5/tengo/compiler/token"
+
+// ArrayIterator is an iterator for an array.
+type ArrayIterator struct {
+	v []Object
+	i int
+	l int
+}
+
+// TypeName returns the name of the type.
+func (i *ArrayIterator) TypeName() string {
+	return "array-iterator"
+}
+
+func (i *ArrayIterator) String() string {
+	return "<array-iterator>"
+}
+
+// BinaryOp returns another object that is the result of
+// a given binary operator and a right-hand side object.
+func (i *ArrayIterator) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	return nil, ErrInvalidOperator
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (i *ArrayIterator) IsFalsy() bool {
+	return true
+}
+
+// Equals returns true if the value of the type
+// is equal to the value of another object.
+func (i *ArrayIterator) Equals(Object) bool {
+	return false
+}
+
+// Copy returns a copy of the type.
+func (i *ArrayIterator) Copy() Object {
+	return &ArrayIterator{v: i.v, i: i.i, l: i.l}
+}
+
+// Next returns true if there are more elements to iterate.
+func (i *ArrayIterator) Next() bool {
+	i.i++
+	return i.i <= i.l
+}
+
+// Key returns the key or index value of the current element.
+func (i *ArrayIterator) Key() Object {
+	return &Int{Value: int64(i.i - 1)}
+}
+
+// Value returns the value of the current element.
+func (i *ArrayIterator) Value() Object {
+	return i.v[i.i-1]
+}
diff --git a/vendor/github.com/d5/tengo/objects/bool.go b/vendor/github.com/d5/tengo/objects/bool.go
new file mode 100644
index 00000000..ac9949e4
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/bool.go
@@ -0,0 +1,64 @@
+package objects
+
+import (
+	"github.com/d5/tengo/compiler/token"
+)
+
+// Bool represents a boolean value.
+type Bool struct {
+	// this is intentionally non-public to force using objects.TrueValue and FalseValue always
+	value bool
+}
+
+func (o *Bool) String() string {
+	if o.value {
+		return "true"
+	}
+
+	return "false"
+}
+
+// TypeName returns the name of the type.
+func (o *Bool) TypeName() string {
+	return "bool"
+}
+
+// BinaryOp returns another object that is the result of
+// a given binary operator and a right-hand side object.
+func (o *Bool) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *Bool) Copy() Object {
+	return o
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *Bool) IsFalsy() bool {
+	return !o.value
+}
+
+// Equals returns true if the value of the type
+// is equal to the value of another object.
+func (o *Bool) Equals(x Object) bool {
+	return o == x
+}
+
+// GobDecode decodes bool value from input bytes.
+func (o *Bool) GobDecode(b []byte) (err error) {
+	o.value = b[0] == 1
+
+	return
+}
+
+// GobEncode encodes bool values into bytes.
+func (o *Bool) GobEncode() (b []byte, err error) {
+	if o.value {
+		b = []byte{1}
+	} else {
+		b = []byte{0}
+	}
+
+	return
+}
diff --git a/vendor/github.com/d5/tengo/objects/break.go b/vendor/github.com/d5/tengo/objects/break.go
new file mode 100644
index 00000000..cd473a87
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/break.go
@@ -0,0 +1,37 @@
+package objects
+
+import "github.com/d5/tengo/compiler/token"
+
+// Break represents a break statement.
+type Break struct{}
+
+// TypeName returns the name of the type.
+func (o *Break) TypeName() string {
+	return "break"
+}
+
+func (o *Break) String() string {
+	return "<break>"
+}
+
+// BinaryOp returns another object that is the result of
+// a given binary operator and a right-hand side object.
+func (o *Break) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *Break) Copy() Object {
+	return &Break{}
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *Break) IsFalsy() bool {
+	return false
+}
+
+// Equals returns true if the value of the type
+// is equal to the value of another object.
+func (o *Break) Equals(x Object) bool {
+	return false
+}
diff --git a/vendor/github.com/d5/tengo/objects/builtin_append.go b/vendor/github.com/d5/tengo/objects/builtin_append.go
new file mode 100644
index 00000000..9fb14b82
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/builtin_append.go
@@ -0,0 +1,21 @@
+package objects
+
+// append(arr, items...)
+func builtinAppend(args ...Object) (Object, error) {
+	if len(args) < 2 {
+		return nil, ErrWrongNumArguments
+	}
+
+	switch arg := args[0].(type) {
+	case *Array:
+		return &Array{Value: append(arg.Value, args[1:]...)}, nil
+	case *ImmutableArray:
+		return &Array{Value: append(arg.Value, args[1:]...)}, nil
+	default:
+		return nil, ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "array",
+			Found:    arg.TypeName(),
+		}
+	}
+}
diff --git a/vendor/github.com/d5/tengo/objects/builtin_convert.go b/vendor/github.com/d5/tengo/objects/builtin_convert.go
new file mode 100644
index 00000000..7d9a8733
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/builtin_convert.go
@@ -0,0 +1,155 @@
+package objects
+
+func builtinString(args ...Object) (Object, error) {
+	argsLen := len(args)
+	if !(argsLen == 1 || argsLen == 2) {
+		return nil, ErrWrongNumArguments
+	}
+
+	if _, ok := args[0].(*String); ok {
+		return args[0], nil
+	}
+
+	v, ok := ToString(args[0])
+	if ok {
+		return &String{Value: v}, nil
+	}
+
+	if argsLen == 2 {
+		return args[1], nil
+	}
+
+	return UndefinedValue, nil
+}
+
+func builtinInt(args ...Object) (Object, error) {
+	argsLen := len(args)
+	if !(argsLen == 1 || argsLen == 2) {
+		return nil, ErrWrongNumArguments
+	}
+
+	if _, ok := args[0].(*Int); ok {
+		return args[0], nil
+	}
+
+	v, ok := ToInt64(args[0])
+	if ok {
+		return &Int{Value: v}, nil
+	}
+
+	if argsLen == 2 {
+		return args[1], nil
+	}
+
+	return UndefinedValue, nil
+}
+
+func builtinFloat(args ...Object) (Object, error) {
+	argsLen := len(args)
+	if !(argsLen == 1 || argsLen == 2) {
+		return nil, ErrWrongNumArguments
+	}
+
+	if _, ok := args[0].(*Float); ok {
+		return args[0], nil
+	}
+
+	v, ok := ToFloat64(args[0])
+	if ok {
+		return &Float{Value: v}, nil
+	}
+
+	if argsLen == 2 {
+		return args[1], nil
+	}
+
+	return UndefinedValue, nil
+}
+
+func builtinBool(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+
+	if _, ok := args[0].(*Bool); ok {
+		return args[0], nil
+	}
+
+	v, ok := ToBool(args[0])
+	if ok {
+		if v {
+			return TrueValue, nil
+		}
+
+		return FalseValue, nil
+	}
+
+	return UndefinedValue, nil
+}
+
+func builtinChar(args ...Object) (Object, error) {
+	argsLen := len(args)
+	if !(argsLen == 1 || argsLen == 2) {
+		return nil, ErrWrongNumArguments
+	}
+
+	if _, ok := args[0].(*Char); ok {
+		return args[0], nil
+	}
+
+	v, ok := ToRune(args[0])
+	if ok {
+		return &Char{Value: v}, nil
+	}
+
+	if argsLen == 2 {
+		return args[1], nil
+	}
+
+	return UndefinedValue, nil
+}
+
+func builtinBytes(args ...Object) (Object, error) {
+	argsLen := len(args)
+	if !(argsLen == 1 || argsLen == 2) {
+		return nil, ErrWrongNumArguments
+	}
+
+	// bytes(N) => create a new bytes with given size N
+	if n, ok := args[0].(*Int); ok {
+		return &Bytes{Value: make([]byte, int(n.Value))}, nil
+	}
+
+	v, ok := ToByteSlice(args[0])
+	if ok {
+		return &Bytes{Value: v}, nil
+	}
+
+	if argsLen == 2 {
+		return args[1], nil
+	}
+
+	return UndefinedValue, nil
+}
+
+func builtinTime(args ...Object) (Object, error) {
+	argsLen := len(args)
+	if !(argsLen == 1 || argsLen == 2) {
+		return nil, ErrWrongNumArguments
+	}
+
+	if _, ok := args[0].(*Time); ok {
+		return args[0], nil
+	}
+
+	v, ok := ToTime(args[0])
+	if ok {
+		return &Time{Value: v}, nil
+	}
+
+	if argsLen == 2 {
+		return args[1], nil
+	}
+
+	return UndefinedValue, nil
+}
diff --git a/vendor/github.com/d5/tengo/objects/builtin_copy.go b/vendor/github.com/d5/tengo/objects/builtin_copy.go
new file mode 100644
index 00000000..4b254b2b
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/builtin_copy.go
@@ -0,0 +1,9 @@
+package objects
+
+func builtinCopy(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+
+	return args[0].Copy(), nil
+}
diff --git a/vendor/github.com/d5/tengo/objects/builtin_function.go b/vendor/github.com/d5/tengo/objects/builtin_function.go
new file mode 100644
index 00000000..1d021617
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/builtin_function.go
@@ -0,0 +1,47 @@
+package objects
+
+import (
+	"github.com/d5/tengo/compiler/token"
+)
+
+// BuiltinFunction represents a builtin function.
+type BuiltinFunction struct {
+	Name  string
+	Value CallableFunc
+}
+
+// TypeName returns the name of the type.
+func (o *BuiltinFunction) TypeName() string {
+	return "builtin-function:" + o.Name
+}
+
+func (o *BuiltinFunction) String() string {
+	return "<builtin-function>"
+}
+
+// BinaryOp returns another object that is the result of
+// a given binary operator and a right-hand side object.
+func (o *BuiltinFunction) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *BuiltinFunction) Copy() Object {
+	return &BuiltinFunction{Value: o.Value}
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *BuiltinFunction) IsFalsy() bool {
+	return false
+}
+
+// Equals returns true if the value of the type
+// is equal to the value of another object.
+func (o *BuiltinFunction) Equals(x Object) bool {
+	return false
+}
+
+// Call executes a builtin function.
+func (o *BuiltinFunction) Call(args ...Object) (Object, error) {
+	return o.Value(args...)
+}
diff --git a/vendor/github.com/d5/tengo/objects/builtin_json.go b/vendor/github.com/d5/tengo/objects/builtin_json.go
new file mode 100644
index 00000000..c0810f7d
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/builtin_json.go
@@ -0,0 +1,54 @@
+package objects
+
+import (
+	"encoding/json"
+)
+
+// to_json(v object) => bytes
+func builtinToJSON(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+
+	res, err := json.Marshal(objectToInterface(args[0]))
+	if err != nil {
+		return &Error{Value: &String{Value: err.Error()}}, nil
+	}
+
+	return &Bytes{Value: res}, nil
+}
+
+// from_json(data string/bytes) => object
+func builtinFromJSON(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+
+	var target interface{}
+
+	switch o := args[0].(type) {
+	case *Bytes:
+		err := json.Unmarshal(o.Value, &target)
+		if err != nil {
+			return &Error{Value: &String{Value: err.Error()}}, nil
+		}
+	case *String:
+		err := json.Unmarshal([]byte(o.Value), &target)
+		if err != nil {
+			return &Error{Value: &String{Value: err.Error()}}, nil
+		}
+	default:
+		return nil, ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "bytes/string",
+			Found:    args[0].TypeName(),
+		}
+	}
+
+	res, err := FromInterface(target)
+	if err != nil {
+		return nil, err
+	}
+
+	return res, nil
+}
diff --git a/vendor/github.com/d5/tengo/objects/builtin_len.go b/vendor/github.com/d5/tengo/objects/builtin_len.go
new file mode 100644
index 00000000..39fbedd8
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/builtin_len.go
@@ -0,0 +1,29 @@
+package objects
+
+// len(obj object) => int
+func builtinLen(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+
+	switch arg := args[0].(type) {
+	case *Array:
+		return &Int{Value: int64(len(arg.Value))}, nil
+	case *ImmutableArray:
+		return &Int{Value: int64(len(arg.Value))}, nil
+	case *String:
+		return &Int{Value: int64(len(arg.Value))}, nil
+	case *Bytes:
+		return &Int{Value: int64(len(arg.Value))}, nil
+	case *Map:
+		return &Int{Value: int64(len(arg.Value))}, nil
+	case *ImmutableMap:
+		return &Int{Value: int64(len(arg.Value))}, nil
+	default:
+		return nil, ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "array/string/bytes/map",
+			Found:    arg.TypeName(),
+		}
+	}
+}
diff --git a/vendor/github.com/d5/tengo/objects/builtin_print.go b/vendor/github.com/d5/tengo/objects/builtin_print.go
new file mode 100644
index 00000000..c5fe36db
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/builtin_print.go
@@ -0,0 +1,75 @@
+package objects
+
+import (
+	"fmt"
+)
+
+// print(args...)
+func builtinPrint(args ...Object) (Object, error) {
+	for _, arg := range args {
+		if str, ok := arg.(*String); ok {
+			fmt.Println(str.Value)
+		} else {
+			fmt.Println(arg.String())
+		}
+	}
+
+	return nil, nil
+}
+
+// printf("format", args...)
+func builtinPrintf(args ...Object) (Object, error) {
+	numArgs := len(args)
+	if numArgs == 0 {
+		return nil, ErrWrongNumArguments
+	}
+
+	format, ok := args[0].(*String)
+	if !ok {
+		return nil, ErrInvalidArgumentType{
+			Name:     "format",
+			Expected: "string",
+			Found:    args[0].TypeName(),
+		}
+	}
+	if numArgs == 1 {
+		fmt.Print(format)
+		return nil, nil
+	}
+
+	formatArgs := make([]interface{}, numArgs-1, numArgs-1)
+	for idx, arg := range args[1:] {
+		formatArgs[idx] = objectToInterface(arg)
+	}
+
+	fmt.Printf(format.Value, formatArgs...)
+
+	return nil, nil
+}
+
+// sprintf("format", args...)
+func builtinSprintf(args ...Object) (Object, error) {
+	numArgs := len(args)
+	if numArgs == 0 {
+		return nil, ErrWrongNumArguments
+	}
+
+	format, ok := args[0].(*String)
+	if !ok {
+		return nil, ErrInvalidArgumentType{
+			Name:     "format",
+			Expected: "string",
+			Found:    args[0].TypeName(),
+		}
+	}
+	if numArgs == 1 {
+		return format, nil // okay to return 'format' directly as String is immutable
+	}
+
+	formatArgs := make([]interface{}, numArgs-1, numArgs-1)
+	for idx, arg := range args[1:] {
+		formatArgs[idx] = objectToInterface(arg)
+	}
+
+	return &String{Value: fmt.Sprintf(format.Value, formatArgs...)}, nil
+}
diff --git a/vendor/github.com/d5/tengo/objects/builtin_type.go b/vendor/github.com/d5/tengo/objects/builtin_type.go
new file mode 100644
index 00000000..376c26bb
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/builtin_type.go
@@ -0,0 +1,9 @@
+package objects
+
+func builtinTypeName(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+
+	return &String{Value: args[0].TypeName()}, nil
+}
diff --git a/vendor/github.com/d5/tengo/objects/builtin_type_checks.go b/vendor/github.com/d5/tengo/objects/builtin_type_checks.go
new file mode 100644
index 00000000..960f7828
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/builtin_type_checks.go
@@ -0,0 +1,183 @@
+package objects
+
+func builtinIsString(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+
+	if _, ok := args[0].(*String); ok {
+		return TrueValue, nil
+	}
+
+	return FalseValue, nil
+}
+
+func builtinIsInt(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+
+	if _, ok := args[0].(*Int); ok {
+		return TrueValue, nil
+	}
+
+	return FalseValue, nil
+}
+
+func builtinIsFloat(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+
+	if _, ok := args[0].(*Float); ok {
+		return TrueValue, nil
+	}
+
+	return FalseValue, nil
+}
+
+func builtinIsBool(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+
+	if _, ok := args[0].(*Bool); ok {
+		return TrueValue, nil
+	}
+
+	return FalseValue, nil
+}
+
+func builtinIsChar(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+
+	if _, ok := args[0].(*Char); ok {
+		return TrueValue, nil
+	}
+
+	return FalseValue, nil
+}
+
+func builtinIsBytes(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+
+	if _, ok := args[0].(*Bytes); ok {
+		return TrueValue, nil
+	}
+
+	return FalseValue, nil
+}
+
+func builtinIsArray(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+
+	if _, ok := args[0].(*Array); ok {
+		return TrueValue, nil
+	}
+
+	return FalseValue, nil
+}
+
+func builtinIsImmutableArray(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+
+	if _, ok := args[0].(*ImmutableArray); ok {
+		return TrueValue, nil
+	}
+
+	return FalseValue, nil
+}
+
+func builtinIsMap(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+
+	if _, ok := args[0].(*Map); ok {
+		return TrueValue, nil
+	}
+
+	return FalseValue, nil
+}
+
+func builtinIsImmutableMap(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+
+	if _, ok := args[0].(*ImmutableMap); ok {
+		return TrueValue, nil
+	}
+
+	return FalseValue, nil
+}
+
+func builtinIsTime(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+
+	if _, ok := args[0].(*Time); ok {
+		return TrueValue, nil
+	}
+
+	return FalseValue, nil
+}
+
+func builtinIsError(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+
+	if _, ok := args[0].(*Error); ok {
+		return TrueValue, nil
+	}
+
+	return FalseValue, nil
+}
+
+func builtinIsUndefined(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+
+	if args[0] == UndefinedValue {
+		return TrueValue, nil
+	}
+
+	return FalseValue, nil
+}
+
+func builtinIsFunction(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+
+	switch args[0].(type) {
+	case *CompiledFunction, *Closure:
+		return TrueValue, nil
+	}
+
+	return FalseValue, nil
+}
+
+func builtinIsCallable(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+
+	switch args[0].(type) {
+	case *CompiledFunction, *Closure, Callable: // BuiltinFunction is Callable
+		return TrueValue, nil
+	}
+
+	return FalseValue, nil
+}
diff --git a/vendor/github.com/d5/tengo/objects/builtins.go b/vendor/github.com/d5/tengo/objects/builtins.go
new file mode 100644
index 00000000..67553932
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/builtins.go
@@ -0,0 +1,135 @@
+package objects
+
+// NamedBuiltinFunc is a named builtin function.
+type NamedBuiltinFunc struct {
+	Name string
+	Func CallableFunc
+}
+
+// Builtins contains all default builtin functions.
+var Builtins = []NamedBuiltinFunc{
+	{
+		Name: "print",
+		Func: builtinPrint,
+	},
+	{
+		Name: "printf",
+		Func: builtinPrintf,
+	},
+	{
+		Name: "sprintf",
+		Func: builtinSprintf,
+	},
+	{
+		Name: "len",
+		Func: builtinLen,
+	},
+	{
+		Name: "copy",
+		Func: builtinCopy,
+	},
+	{
+		Name: "append",
+		Func: builtinAppend,
+	},
+	{
+		Name: "string",
+		Func: builtinString,
+	},
+	{
+		Name: "int",
+		Func: builtinInt,
+	},
+	{
+		Name: "bool",
+		Func: builtinBool,
+	},
+	{
+		Name: "float",
+		Func: builtinFloat,
+	},
+	{
+		Name: "char",
+		Func: builtinChar,
+	},
+	{
+		Name: "bytes",
+		Func: builtinBytes,
+	},
+	{
+		Name: "time",
+		Func: builtinTime,
+	},
+	{
+		Name: "is_int",
+		Func: builtinIsInt,
+	},
+	{
+		Name: "is_float",
+		Func: builtinIsFloat,
+	},
+	{
+		Name: "is_string",
+		Func: builtinIsString,
+	},
+	{
+		Name: "is_bool",
+		Func: builtinIsBool,
+	},
+	{
+		Name: "is_char",
+		Func: builtinIsChar,
+	},
+	{
+		Name: "is_bytes",
+		Func: builtinIsBytes,
+	},
+	{
+		Name: "is_array",
+		Func: builtinIsArray,
+	},
+	{
+		Name: "is_immutable_array",
+		Func: builtinIsImmutableArray,
+	},
+	{
+		Name: "is_map",
+		Func: builtinIsMap,
+	},
+	{
+		Name: "is_immutable_map",
+		Func: builtinIsImmutableMap,
+	},
+	{
+		Name: "is_time",
+		Func: builtinIsTime,
+	},
+	{
+		Name: "is_error",
+		Func: builtinIsError,
+	},
+	{
+		Name: "is_undefined",
+		Func: builtinIsUndefined,
+	},
+	{
+		Name: "is_function",
+		Func: builtinIsFunction,
+	},
+	{
+		Name: "is_callable",
+		Func: builtinIsCallable,
+	},
+	{
+		Name: "to_json",
+		Func: builtinToJSON,
+	},
+	{
+		Name: "from_json",
+		Func: builtinFromJSON,
+	},
+	{
+		Name: "type_name",
+		Func: builtinTypeName,
+	},
+}
diff --git a/vendor/github.com/d5/tengo/objects/bytes.go b/vendor/github.com/d5/tengo/objects/bytes.go
new file mode 100644
index 00000000..7d8d6694
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/bytes.go
@@ -0,0 +1,76 @@
+package objects
+
+import (
+	"bytes"
+
+	"github.com/d5/tengo/compiler/token"
+)
+
+// Bytes represents a byte array.
+type Bytes struct {
+	Value []byte
+}
+
+func (o *Bytes) String() string {
+	return string(o.Value)
+}
+
+// TypeName returns the name of the type.
+func (o *Bytes) TypeName() string {
+	return "bytes"
+}
+
+// BinaryOp returns another object that is the result of
+// a given binary operator and a right-hand side object.
+func (o *Bytes) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	switch op {
+	case token.Add:
+		switch rhs := rhs.(type) {
+		case *Bytes:
+			return &Bytes{Value: append(o.Value, rhs.Value...)}, nil
+		}
+	}
+
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *Bytes) Copy() Object {
+	return &Bytes{Value: append([]byte{}, o.Value...)}
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *Bytes) IsFalsy() bool {
+	return len(o.Value) == 0
+}
+
+// Equals returns true if the value of the type
+// is equal to the value of another object.
+func (o *Bytes) Equals(x Object) bool {
+	t, ok := x.(*Bytes)
+	if !ok {
+		return false
+	}
+
+	return bytes.Compare(o.Value, t.Value) == 0
+}
+
+// IndexGet returns an element (as Int) at a given index.
+func (o *Bytes) IndexGet(index Object) (res Object, err error) {
+	intIdx, ok := index.(*Int)
+	if !ok {
+		err = ErrInvalidIndexType
+		return
+	}
+
+	idxVal := int(intIdx.Value)
+
+	if idxVal < 0 || idxVal >= len(o.Value) {
+		res = UndefinedValue
+		return
+	}
+
+	res = &Int{Value: int64(o.Value[idxVal])}
+
+	return
+}
diff --git a/vendor/github.com/d5/tengo/objects/callable.go b/vendor/github.com/d5/tengo/objects/callable.go
new file mode 100644
index 00000000..a066e1b9
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/callable.go
@@ -0,0 +1,9 @@
+package objects
+
+// Callable represents an object that can be called like a function.
+type Callable interface {
+	// Call should take an arbitrary number of arguments
+	// and returns a return value and/or an error,
+	// which the VM will consider as a run-time error.
+	Call(args ...Object) (ret Object, err error)
+}
diff --git a/vendor/github.com/d5/tengo/objects/callable_func.go b/vendor/github.com/d5/tengo/objects/callable_func.go
new file mode 100644
index 00000000..cf9b43aa
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/callable_func.go
@@ -0,0 +1,4 @@
+package objects
+
+// CallableFunc is a function signature for the callable functions.
+type CallableFunc func(args ...Object) (ret Object, err error)
diff --git a/vendor/github.com/d5/tengo/objects/char.go b/vendor/github.com/d5/tengo/objects/char.go
new file mode 100644
index 00000000..4458bd12
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/char.go
@@ -0,0 +1,119 @@
+package objects
+
+import (
+	"github.com/d5/tengo/compiler/token"
+)
+
+// Char represents a character value.
+type Char struct {
+	Value rune
+}
+
+func (o *Char) String() string {
+	return string(o.Value)
+}
+
+// TypeName returns the name of the type.
+func (o *Char) TypeName() string {
+	return "char"
+}
+
+// BinaryOp returns another object that is the result of
+// a given binary operator and a right-hand side object.
+func (o *Char) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	switch rhs := rhs.(type) {
+	case *Char:
+		switch op {
+		case token.Add:
+			r := o.Value + rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Char{Value: r}, nil
+		case token.Sub:
+			r := o.Value - rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Char{Value: r}, nil
+		case token.Less:
+			if o.Value < rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.Greater:
+			if o.Value > rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.LessEq:
+			if o.Value <= rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.GreaterEq:
+			if o.Value >= rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		}
+	case *Int:
+		switch op {
+		case token.Add:
+			r := o.Value + rune(rhs.Value)
+			if r == o.Value {
+				return o, nil
+			}
+			return &Char{Value: r}, nil
+		case token.Sub:
+			r := o.Value - rune(rhs.Value)
+			if r == o.Value {
+				return o, nil
+			}
+			return &Char{Value: r}, nil
+		case token.Less:
+			if int64(o.Value) < rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.Greater:
+			if int64(o.Value) > rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.LessEq:
+			if int64(o.Value) <= rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.GreaterEq:
+			if int64(o.Value) >= rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		}
+	}
+
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *Char) Copy() Object {
+	return &Char{Value: o.Value}
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *Char) IsFalsy() bool {
+	return o.Value == 0
+}
+
+// Equals returns true if the value of the type
+// is equal to the value of another object.
+func (o *Char) Equals(x Object) bool {
+	t, ok := x.(*Char)
+	if !ok {
+		return false
+	}
+
+	return o.Value == t.Value
+}
diff --git a/vendor/github.com/d5/tengo/objects/closure.go b/vendor/github.com/d5/tengo/objects/closure.go
new file mode 100644
index 00000000..d4915a52
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/closure.go
@@ -0,0 +1,45 @@
+package objects
+
+import (
+	"github.com/d5/tengo/compiler/token"
+)
+
+// Closure represents a function closure.
+type Closure struct {
+	Fn   *CompiledFunction
+	Free []*Object
+}
+
+// TypeName returns the name of the type.
+func (o *Closure) TypeName() string {
+	return "closure"
+}
+
+func (o *Closure) String() string {
+	return "<closure>"
+}
+
+// BinaryOp returns another object that is the result of
+// a given binary operator and a right-hand side object.
+func (o *Closure) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *Closure) Copy() Object {
+	return &Closure{
+		Fn:   o.Fn.Copy().(*CompiledFunction),
+		Free: append([]*Object{}, o.Free...), // DO NOT Copy() of elements; these are variable pointers
+	}
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *Closure) IsFalsy() bool {
+	return false
+}
+
+// Equals returns true if the value of the type
+// is equal to the value of another object.
+func (o *Closure) Equals(x Object) bool {
+	return false
+}
diff --git a/vendor/github.com/d5/tengo/objects/compiled_function.go b/vendor/github.com/d5/tengo/objects/compiled_function.go
new file mode 100644
index 00000000..d20f2375
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/compiled_function.go
@@ -0,0 +1,49 @@
+package objects
+
+import (
+	"github.com/d5/tengo/compiler/source"
+	"github.com/d5/tengo/compiler/token"
+)
+
+// CompiledFunction represents a compiled function.
+type CompiledFunction struct {
+	Instructions  []byte
+	NumLocals     int // number of local variables (including function parameters)
+	NumParameters int
+	SourceMap     map[int]source.Pos
+}
+
+// TypeName returns the name of the type.
+func (o *CompiledFunction) TypeName() string {
+	return "compiled-function"
+}
+
+func (o *CompiledFunction) String() string {
+	return "<compiled-function>"
+}
+
+// BinaryOp returns another object that is the result of
+// a given binary operator and a right-hand side object.
+func (o *CompiledFunction) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *CompiledFunction) Copy() Object {
+	return &CompiledFunction{
+		Instructions:  append([]byte{}, o.Instructions...),
+		NumLocals:     o.NumLocals,
+		NumParameters: o.NumParameters,
+	}
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *CompiledFunction) IsFalsy() bool {
+	return false
+}
+
+// Equals returns true if the value of the type
+// is equal to the value of another object.
+func (o *CompiledFunction) Equals(x Object) bool {
+	return false
+}
diff --git a/vendor/github.com/d5/tengo/objects/continue.go b/vendor/github.com/d5/tengo/objects/continue.go
new file mode 100644
index 00000000..8094e686
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/continue.go
@@ -0,0 +1,38 @@
+package objects
+
+import "github.com/d5/tengo/compiler/token"
+
+// Continue represents a continue statement.
+type Continue struct {
+}
+
+// TypeName returns the name of the type.
+func (o *Continue) TypeName() string {
+	return "continue"
+}
+
+func (o *Continue) String() string {
+	return "<continue>"
+}
+
+// BinaryOp returns another object that is the result of
+// a given binary operator and a right-hand side object.
+func (o *Continue) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *Continue) Copy() Object {
+	return &Continue{}
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *Continue) IsFalsy() bool {
+	return false
+}
+
+// Equals returns true if the value of the type
+// is equal to the value of another object.
+func (o *Continue) Equals(x Object) bool {
+	return false
+}
diff --git a/vendor/github.com/d5/tengo/objects/conversion.go b/vendor/github.com/d5/tengo/objects/conversion.go
new file mode 100644
index 00000000..3c17546f
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/conversion.go
@@ -0,0 +1,249 @@
+package objects
+
+import (
+	"fmt"
+	"strconv"
+	"time"
+)
+
+// ToString will try to convert object o to string value.
+func ToString(o Object) (v string, ok bool) {
+	if o == UndefinedValue {
+		//ok = false
+		return
+	}
+
+	ok = true
+
+	if str, isStr := o.(*String); isStr {
+		v = str.Value
+	} else {
+		v = o.String()
+	}
+
+	return
+}
+
+// ToInt will try to convert object o to int value.
+func ToInt(o Object) (v int, ok bool) {
+	switch o := o.(type) {
+	case *Int:
+		v = int(o.Value)
+		ok = true
+	case *Float:
+		v = int(o.Value)
+		ok = true
+	case *Char:
+		v = int(o.Value)
+		ok = true
+	case *Bool:
+		if o == TrueValue {
+			v = 1
+		}
+		ok = true
+	case *String:
+		c, err := strconv.ParseInt(o.Value, 10, 64)
+		if err == nil {
+			v = int(c)
+			ok = true
+		}
+	}
+
+	//ok = false
+	return
+}
+
+// ToInt64 will try to convert object o to int64 value.
+func ToInt64(o Object) (v int64, ok bool) {
+	switch o := o.(type) {
+	case *Int:
+		v = o.Value
+		ok = true
+	case *Float:
+		v = int64(o.Value)
+		ok = true
+	case *Char:
+		v = int64(o.Value)
+		ok = true
+	case *Bool:
+		if o == TrueValue {
+			v = 1
+		}
+		ok = true
+	case *String:
+		c, err := strconv.ParseInt(o.Value, 10, 64)
+		if err == nil {
+			v = c
+			ok = true
+		}
+	}
+
+	//ok = false
+	return
+}
+
+// ToFloat64 will try to convert object o to float64 value.
+func ToFloat64(o Object) (v float64, ok bool) {
+	switch o := o.(type) {
+	case *Int:
+		v = float64(o.Value)
+		ok = true
+	case *Float:
+		v = o.Value
+		ok = true
+	case *String:
+		c, err := strconv.ParseFloat(o.Value, 64)
+		if err == nil {
+			v = c
+			ok = true
+		}
+	}
+
+	//ok = false
+	return
+}
+
+// ToBool will try to convert object o to bool value.
+func ToBool(o Object) (v bool, ok bool) {
+	ok = true
+	v = !o.IsFalsy()
+
+	return
+}
+
+// ToRune will try to convert object o to rune value.
+func ToRune(o Object) (v rune, ok bool) {
+	switch o := o.(type) {
+	case *Int:
+		v = rune(o.Value)
+		ok = true
+	case *Char:
+		v = rune(o.Value)
+		ok = true
+	}
+
+	//ok = false
+	return
+}
+
+// ToByteSlice will try to convert object o to []byte value.
+func ToByteSlice(o Object) (v []byte, ok bool) {
+	switch o := o.(type) {
+	case *Bytes:
+		v = o.Value
+		ok = true
+	case *String:
+		v = []byte(o.Value)
+		ok = true
+	}
+
+	//ok = false
+	return
+}
+
+// ToTime will try to convert object o to time.Time value.
+func ToTime(o Object) (v time.Time, ok bool) {
+	switch o := o.(type) {
+	case *Time:
+		v = o.Value
+		ok = true
+	case *Int:
+		v = time.Unix(o.Value, 0)
+		ok = true
+	}
+
+	//ok = false
+	return
+}
+
+// objectToInterface attempts to convert an object o to an interface{} value
+func objectToInterface(o Object) (res interface{}) {
+	switch o := o.(type) {
+	case *Int:
+		res = o.Value
+	case *String:
+		res = o.Value
+	case *Float:
+		res = o.Value
+	case *Bool:
+		res = o == TrueValue
+	case *Char:
+		res = o.Value
+	case *Bytes:
+		res = o.Value
+	case *Array:
+		res = make([]interface{}, len(o.Value))
+		for i, val := range o.Value {
+			res.([]interface{})[i] = objectToInterface(val)
+		}
+	case *Map:
+		res = make(map[string]interface{})
+		for key, v := range o.Value {
+			res.(map[string]interface{})[key] = objectToInterface(v)
+		}
+	case Object:
+		return o
+	}
+
+	return
+}
+
+// FromInterface will attempt to convert an interface{} v to a Tengo Object
+func FromInterface(v interface{}) (Object, error) {
+	switch v := v.(type) {
+	case nil:
+		return UndefinedValue, nil
+	case string:
+		return &String{Value: v}, nil
+	case int64:
+		return &Int{Value: v}, nil
+	case int:
+		return &Int{Value: int64(v)}, nil
+	case bool:
+		if v {
+			return TrueValue, nil
+		}
+		return FalseValue, nil
+	case rune:
+		return &Char{Value: v}, nil
+	case byte:
+		return &Char{Value: rune(v)}, nil
+	case float64:
+		return &Float{Value: v}, nil
+	case []byte:
+		return &Bytes{Value: v}, nil
+	case error:
+		return &Error{Value: &String{Value: v.Error()}}, nil
+	case map[string]Object:
+		return &Map{Value: v}, nil
+	case map[string]interface{}:
+		kv := make(map[string]Object)
+		for vk, vv := range v {
+			vo, err := FromInterface(vv)
+			if err != nil {
+				return nil, err
+			}
+			kv[vk] = vo
+		}
+		return &Map{Value: kv}, nil
+	case []Object:
+		return &Array{Value: v}, nil
+	case []interface{}:
+		arr := make([]Object, len(v), len(v))
+		for i, e := range v {
+			vo, err := FromInterface(e)
+			if err != nil {
+				return nil, err
+			}
+
+			arr[i] = vo
+		}
+		return &Array{Value: arr}, nil
+	case time.Time:
+		return &Time{Value: v}, nil
+	case Object:
+		return v, nil
+	}
+
+	return nil, fmt.Errorf("cannot convert to object: %T", v)
+}
diff --git a/vendor/github.com/d5/tengo/objects/error.go b/vendor/github.com/d5/tengo/objects/error.go
new file mode 100644
index 00000000..be21de03
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/error.go
@@ -0,0 +1,47 @@
+package objects
+
+import (
+	"fmt"
+
+	"github.com/d5/tengo/compiler/token"
+)
+
+// Error represents a string value.
+type Error struct {
+	Value Object
+}
+
+// TypeName returns the name of the type.
+func (o *Error) TypeName() string {
+	return "error"
+}
+
+func (o *Error) String() string {
+	if o.Value != nil {
+		return fmt.Sprintf("error: %s", o.Value.String())
+	}
+
+	return "error"
+}
+
+// BinaryOp returns another object that is the result of
+// a given binary operator and a right-hand side object.
+func (o *Error) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	return nil, ErrInvalidOperator
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *Error) IsFalsy() bool {
+	return true // error is always false.
+}
+
+// Copy returns a copy of the type.
+func (o *Error) Copy() Object {
+	return &Error{Value: o.Value.Copy()}
+}
+
+// Equals returns true if the value of the type
+// is equal to the value of another object.
+func (o *Error) Equals(x Object) bool {
+	return o == x // pointer equality
+}
diff --git a/vendor/github.com/d5/tengo/objects/errors.go b/vendor/github.com/d5/tengo/objects/errors.go
new file mode 100644
index 00000000..e4012314
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/errors.go
@@ -0,0 +1,32 @@
+package objects
+
+import (
+	"errors"
+	"fmt"
+)
+
+// ErrIndexOutOfBounds is an error where a given index is out of the bounds.
+var ErrIndexOutOfBounds = errors.New("index out of bounds")
+
+// ErrInvalidIndexType represents an invalid index type.
+var ErrInvalidIndexType = errors.New("invalid index type")
+
+// ErrInvalidIndexValueType represents an invalid index value type.
+var ErrInvalidIndexValueType = errors.New("invalid index value type")
+
+// ErrInvalidOperator represents an error for invalid operator usage.
+var ErrInvalidOperator = errors.New("invalid operator")
+
+// ErrWrongNumArguments represents a wrong number of arguments error.
+var ErrWrongNumArguments = errors.New("wrong number of arguments")
+
+// ErrInvalidArgumentType represents an invalid argument value type error.
+type ErrInvalidArgumentType struct {
+	Name     string
+	Expected string
+	Found    string
+}
+
+func (e ErrInvalidArgumentType) Error() string {
+	return fmt.Sprintf("invalid type for argument '%s': expected %s, found %s", e.Name, e.Expected, e.Found)
+}
diff --git a/vendor/github.com/d5/tengo/objects/float.go b/vendor/github.com/d5/tengo/objects/float.go
new file mode 100644
index 00000000..65997303
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/float.go
@@ -0,0 +1,146 @@
+package objects
+
+import (
+	"math"
+	"strconv"
+
+	"github.com/d5/tengo/compiler/token"
+)
+
+// Float represents a floating point number value.
+type Float struct {
+	Value float64
+}
+
+func (o *Float) String() string {
+	return strconv.FormatFloat(o.Value, 'f', -1, 64)
+}
+
+// TypeName returns the name of the type.
+func (o *Float) TypeName() string {
+	return "float"
+}
+
+// BinaryOp returns another object that is the result of
+// a given binary operator and a right-hand side object.
+func (o *Float) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	switch rhs := rhs.(type) {
+	case *Float:
+		switch op {
+		case token.Add:
+			r := o.Value + rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Float{Value: r}, nil
+		case token.Sub:
+			r := o.Value - rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Float{Value: r}, nil
+		case token.Mul:
+			r := o.Value * rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Float{Value: r}, nil
+		case token.Quo:
+			r := o.Value / rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Float{Value: r}, nil
+		case token.Less:
+			if o.Value < rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.Greater:
+			if o.Value > rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.LessEq:
+			if o.Value <= rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.GreaterEq:
+			if o.Value >= rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		}
+	case *Int:
+		switch op {
+		case token.Add:
+			r := o.Value + float64(rhs.Value)
+			if r == o.Value {
+				return o, nil
+			}
+			return &Float{Value: r}, nil
+		case token.Sub:
+			r := o.Value - float64(rhs.Value)
+			if r == o.Value {
+				return o, nil
+			}
+			return &Float{Value: r}, nil
+		case token.Mul:
+			r := o.Value * float64(rhs.Value)
+			if r == o.Value {
+				return o, nil
+			}
+			return &Float{Value: r}, nil
+		case token.Quo:
+			r := o.Value / float64(rhs.Value)
+			if r == o.Value {
+				return o, nil
+			}
+			return &Float{Value: r}, nil
+		case token.Less:
+			if o.Value < float64(rhs.Value) {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.Greater:
+			if o.Value > float64(rhs.Value) {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.LessEq:
+			if o.Value <= float64(rhs.Value) {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.GreaterEq:
+			if o.Value >= float64(rhs.Value) {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		}
+	}
+
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *Float) Copy() Object {
+	return &Float{Value: o.Value}
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *Float) IsFalsy() bool {
+	return math.IsNaN(o.Value)
+}
+
+// Equals returns true if the value of the type
+// is equal to the value of another object.
+func (o *Float) Equals(x Object) bool {
+	t, ok := x.(*Float)
+	if !ok {
+		return false
+	}
+
+	return o.Value == t.Value
+}
diff --git a/vendor/github.com/d5/tengo/objects/immautable_array.go b/vendor/github.com/d5/tengo/objects/immautable_array.go
new file mode 100644
index 00000000..f3621e29
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/immautable_array.go
@@ -0,0 +1,109 @@
+package objects
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/d5/tengo/compiler/token"
+)
+
+// ImmutableArray represents an immutable array of objects.
+type ImmutableArray struct {
+	Value []Object
+}
+
+// TypeName returns the name of the type.
+func (o *ImmutableArray) TypeName() string {
+	return "immutable-array"
+}
+
+func (o *ImmutableArray) String() string {
+	var elements []string
+	for _, e := range o.Value {
+		elements = append(elements, e.String())
+	}
+
+	return fmt.Sprintf("[%s]", strings.Join(elements, ", "))
+}
+
+// BinaryOp returns another object that is the result of
+// a given binary operator and a right-hand side object.
+func (o *ImmutableArray) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	if rhs, ok := rhs.(*ImmutableArray); ok {
+		switch op {
+		case token.Add:
+			return &Array{Value: append(o.Value, rhs.Value...)}, nil
+		}
+	}
+
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *ImmutableArray) Copy() Object {
+	var c []Object
+	for _, elem := range o.Value {
+		c = append(c, elem.Copy())
+	}
+
+	return &Array{Value: c}
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *ImmutableArray) IsFalsy() bool {
+	return len(o.Value) == 0
+}
+
+// Equals returns true if the value of the type
+// is equal to the value of another object.
+func (o *ImmutableArray) Equals(x Object) bool {
+	var xVal []Object
+	switch x := x.(type) {
+	case *Array:
+		xVal = x.Value
+	case *ImmutableArray:
+		xVal = x.Value
+	default:
+		return false
+	}
+
+	if len(o.Value) != len(xVal) {
+		return false
+	}
+
+	for i, e := range o.Value {
+		if !e.Equals(xVal[i]) {
+			return false
+		}
+	}
+
+	return true
+}
+
+// IndexGet returns an element at a given index.
+func (o *ImmutableArray) IndexGet(index Object) (res Object, err error) {
+	intIdx, ok := index.(*Int)
+	if !ok {
+		err = ErrInvalidIndexType
+		return
+	}
+
+	idxVal := int(intIdx.Value)
+
+	if idxVal < 0 || idxVal >= len(o.Value) {
+		res = UndefinedValue
+		return
+	}
+
+	res = o.Value[idxVal]
+
+	return
+}
+
+// Iterate creates an array iterator.
+func (o *ImmutableArray) Iterate() Iterator {
+	return &ArrayIterator{
+		v: o.Value,
+		l: len(o.Value),
+	}
+}
diff --git a/vendor/github.com/d5/tengo/objects/immutable_map.go b/vendor/github.com/d5/tengo/objects/immutable_map.go
new file mode 100644
index 00000000..8f58701b
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/immutable_map.go
@@ -0,0 +1,105 @@
+package objects
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/d5/tengo/compiler/token"
+)
+
+// ImmutableMap represents an immutable map object.
+type ImmutableMap struct {
+	Value map[string]Object
+}
+
+// TypeName returns the name of the type.
+func (o *ImmutableMap) TypeName() string {
+	return "immutable-map"
+}
+
+func (o *ImmutableMap) String() string {
+	var pairs []string
+	for k, v := range o.Value {
+		pairs = append(pairs, fmt.Sprintf("%s: %s", k, v.String()))
+	}
+
+	return fmt.Sprintf("{%s}", strings.Join(pairs, ", "))
+}
+
+// BinaryOp returns another object that is the result of
+// a given binary operator and a right-hand side object.
+func (o *ImmutableMap) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *ImmutableMap) Copy() Object {
+	c := make(map[string]Object)
+	for k, v := range o.Value {
+		c[k] = v.Copy()
+	}
+
+	return &Map{Value: c}
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *ImmutableMap) IsFalsy() bool {
+	return len(o.Value) == 0
+}
+
+// IndexGet returns the value for the given key.
+func (o *ImmutableMap) IndexGet(index Object) (res Object, err error) {
+	strIdx, ok := ToString(index)
+	if !ok {
+		err = ErrInvalidIndexType
+		return
+	}
+
+	val, ok := o.Value[strIdx]
+	if !ok {
+		val = UndefinedValue
+	}
+
+	return val, nil
+}
+
+// Equals returns true if the value of the type
+// is equal to the value of another object.
+func (o *ImmutableMap) Equals(x Object) bool {
+	var xVal map[string]Object
+	switch x := x.(type) {
+	case *Map:
+		xVal = x.Value
+	case *ImmutableMap:
+		xVal = x.Value
+	default:
+		return false
+	}
+
+	if len(o.Value) != len(xVal) {
+		return false
+	}
+
+	for k, v := range o.Value {
+		tv := xVal[k]
+		if !v.Equals(tv) {
+			return false
+		}
+	}
+
+	return true
+}
+
+// Iterate creates an immutable map iterator.
+func (o *ImmutableMap) Iterate() Iterator {
+	var keys []string
+	for k := range o.Value {
+		keys = append(keys, k)
+	}
+
+	return &MapIterator{
+		v: o.Value,
+		k: keys,
+		l: len(keys),
+	}
+}
diff --git a/vendor/github.com/d5/tengo/objects/index_assignable.go b/vendor/github.com/d5/tengo/objects/index_assignable.go
new file mode 100644
index 00000000..a1c6cbff
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/index_assignable.go
@@ -0,0 +1,9 @@
+package objects
+
+// IndexAssignable is an object that can take an index and a value
+// on the left-hand side of the assignment statement.
+type IndexAssignable interface {
+	// IndexSet should take an index Object and a value Object.
+	// If an error is returned, it will be treated as a run-time error.
+	IndexSet(index, value Object) error
+}
diff --git a/vendor/github.com/d5/tengo/objects/indexable.go b/vendor/github.com/d5/tengo/objects/indexable.go
new file mode 100644
index 00000000..bbc81633
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/indexable.go
@@ -0,0 +1,9 @@
+package objects
+
+// Indexable is an object that can take an index and return an object.
+type Indexable interface {
+	// IndexGet should take an index Object and return a result Object or an error.
+	// If error is returned, the runtime will treat it as a run-time error and ignore returned value.
+	// If nil is returned as value, it will be converted to Undefined value by the runtime.
+	IndexGet(index Object) (value Object, err error)
+}
diff --git a/vendor/github.com/d5/tengo/objects/int.go b/vendor/github.com/d5/tengo/objects/int.go
new file mode 100644
index 00000000..e902c93a
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/int.go
@@ -0,0 +1,198 @@
+package objects
+
+import (
+	"strconv"
+
+	"github.com/d5/tengo/compiler/token"
+)
+
+// Int represents an integer value.
+type Int struct {
+	Value int64
+}
+
+func (o *Int) String() string {
+	return strconv.FormatInt(o.Value, 10)
+}
+
+// TypeName returns the name of the type.
+func (o *Int) TypeName() string {
+	return "int"
+}
+
+// BinaryOp returns another object that is the result of
+// a given binary operator and a right-hand side object.
+func (o *Int) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	switch rhs := rhs.(type) {
+	case *Int:
+		switch op {
+		case token.Add:
+			r := o.Value + rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Int{Value: r}, nil
+		case token.Sub:
+			r := o.Value - rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Int{Value: r}, nil
+		case token.Mul:
+			r := o.Value * rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Int{Value: r}, nil
+		case token.Quo:
+			r := o.Value / rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Int{Value: r}, nil
+		case token.Rem:
+			r := o.Value % rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Int{Value: r}, nil
+		case token.And:
+			r := o.Value & rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Int{Value: r}, nil
+		case token.Or:
+			r := o.Value | rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Int{Value: r}, nil
+		case token.Xor:
+			r := o.Value ^ rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Int{Value: r}, nil
+		case token.AndNot:
+			r := o.Value &^ rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Int{Value: r}, nil
+		case token.Shl:
+			r := o.Value << uint64(rhs.Value)
+			if r == o.Value {
+				return o, nil
+			}
+			return &Int{Value: r}, nil
+		case token.Shr:
+			r := o.Value >> uint64(rhs.Value)
+			if r == o.Value {
+				return o, nil
+			}
+			return &Int{Value: r}, nil
+		case token.Less:
+			if o.Value < rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.Greater:
+			if o.Value > rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.LessEq:
+			if o.Value <= rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.GreaterEq:
+			if o.Value >= rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		}
+	case *Float:
+		switch op {
+		case token.Add:
+			return &Float{float64(o.Value) + rhs.Value}, nil
+		case token.Sub:
+			return &Float{float64(o.Value) - rhs.Value}, nil
+		case token.Mul:
+			return &Float{float64(o.Value) * rhs.Value}, nil
+		case token.Quo:
+			return &Float{float64(o.Value) / rhs.Value}, nil
+		case token.Less:
+			if float64(o.Value) < rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.Greater:
+			if float64(o.Value) > rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.LessEq:
+			if float64(o.Value) <= rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.GreaterEq:
+			if float64(o.Value) >= rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		}
+	case *Char:
+		switch op {
+		case token.Add:
+			return &Char{rune(o.Value) + rhs.Value}, nil
+		case token.Sub:
+			return &Char{rune(o.Value) - rhs.Value}, nil
+		case token.Less:
+			if o.Value < int64(rhs.Value) {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.Greater:
+			if o.Value > int64(rhs.Value) {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.LessEq:
+			if o.Value <= int64(rhs.Value) {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.GreaterEq:
+			if o.Value >= int64(rhs.Value) {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		}
+	}
+
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *Int) Copy() Object {
+	return &Int{Value: o.Value}
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *Int) IsFalsy() bool {
+	return o.Value == 0
+}
+
+// Equals returns true if the value of the type
+// is equal to the value of another object.
+func (o *Int) Equals(x Object) bool {
+	t, ok := x.(*Int)
+	if !ok {
+		return false
+	}
+
+	return o.Value == t.Value
+}
diff --git a/vendor/github.com/d5/tengo/objects/iterable.go b/vendor/github.com/d5/tengo/objects/iterable.go
new file mode 100644
index 00000000..e431d3d7
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/iterable.go
@@ -0,0 +1,7 @@
+package objects
+
+// Iterable represents an object that has iterator.
+type Iterable interface {
+	// Iterate should return an Iterator for the type.
+	Iterate() Iterator
+}
diff --git a/vendor/github.com/d5/tengo/objects/iterator.go b/vendor/github.com/d5/tengo/objects/iterator.go
new file mode 100644
index 00000000..01522ba5
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/iterator.go
@@ -0,0 +1,15 @@
+package objects
+
+// Iterator represents an iterator for underlying data type.
+type Iterator interface {
+	Object
+
+	// Next returns true if there are more elements to iterate.
+	Next() bool
+
+	// Key returns the key or index value of the current element.
+	Key() Object
+
+	// Value returns the value of the current element.
+	Value() Object
+}
diff --git a/vendor/github.com/d5/tengo/objects/map.go b/vendor/github.com/d5/tengo/objects/map.go
new file mode 100644
index 00000000..c42ffe93
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/map.go
@@ -0,0 +1,118 @@
+package objects
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/d5/tengo/compiler/token"
+)
+
+// Map represents a map of objects.
+type Map struct {
+	Value map[string]Object
+}
+
+// TypeName returns the name of the type.
+func (o *Map) TypeName() string {
+	return "map"
+}
+
+func (o *Map) String() string {
+	var pairs []string
+	for k, v := range o.Value {
+		pairs = append(pairs, fmt.Sprintf("%s: %s", k, v.String()))
+	}
+
+	return fmt.Sprintf("{%s}", strings.Join(pairs, ", "))
+}
+
+// BinaryOp returns another object that is the result of
+// a given binary operator and a right-hand side object.
+func (o *Map) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *Map) Copy() Object {
+	c := make(map[string]Object)
+	for k, v := range o.Value {
+		c[k] = v.Copy()
+	}
+
+	return &Map{Value: c}
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *Map) IsFalsy() bool {
+	return len(o.Value) == 0
+}
+
+// Equals returns true if the value of the type
+// is equal to the value of another object.
+func (o *Map) Equals(x Object) bool {
+	var xVal map[string]Object
+	switch x := x.(type) {
+	case *Map:
+		xVal = x.Value
+	case *ImmutableMap:
+		xVal = x.Value
+	default:
+		return false
+	}
+
+	if len(o.Value) != len(xVal) {
+		return false
+	}
+
+	for k, v := range o.Value {
+		tv := xVal[k]
+		if !v.Equals(tv) {
+			return false
+		}
+	}
+
+	return true
+}
+
+// IndexGet returns the value for the given key.
+func (o *Map) IndexGet(index Object) (res Object, err error) {
+	strIdx, ok := index.(*String)
+	if !ok {
+		err = ErrInvalidIndexType
+		return
+	}
+
+	val, ok := o.Value[strIdx.Value]
+	if !ok {
+		val = UndefinedValue
+	}
+
+	return val, nil
+}
+
+// IndexSet sets the value for the given key.
+func (o *Map) IndexSet(index, value Object) (err error) {
+	strIdx, ok := ToString(index)
+	if !ok {
+		err = ErrInvalidIndexType
+		return
+	}
+
+	o.Value[strIdx] = value
+
+	return nil
+}
+
+// Iterate creates a map iterator.
+func (o *Map) Iterate() Iterator {
+	var keys []string
+	for k := range o.Value {
+		keys = append(keys, k)
+	}
+
+	return &MapIterator{
+		v: o.Value,
+		k: keys,
+		l: len(keys),
+	}
+}
diff --git a/vendor/github.com/d5/tengo/objects/map_iterator.go b/vendor/github.com/d5/tengo/objects/map_iterator.go
new file mode 100644
index 00000000..d60dd0e1
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/map_iterator.go
@@ -0,0 +1,62 @@
+package objects
+
+import "github.com/d5/tengo/compiler/token"
+
+// MapIterator represents an iterator for the map.
+type MapIterator struct {
+	v map[string]Object
+	k []string
+	i int
+	l int
+}
+
+// TypeName returns the name of the type.
+func (i *MapIterator) TypeName() string {
+	return "map-iterator"
+}
+
+func (i *MapIterator) String() string {
+	return "<map-iterator>"
+}
+
+// BinaryOp returns another object that is the result of
+// a given binary operator and a right-hand side object.
+func (i *MapIterator) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	return nil, ErrInvalidOperator
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (i *MapIterator) IsFalsy() bool {
+	return true
+}
+
+// Equals returns true if the value of the type
+// is equal to the value of another object.
+func (i *MapIterator) Equals(Object) bool {
+	return false
+}
+
+// Copy returns a copy of the type.
+func (i *MapIterator) Copy() Object {
+	return &MapIterator{v: i.v, k: i.k, i: i.i, l: i.l}
+}
+
+// Next returns true if there are more elements to iterate.
+func (i *MapIterator) Next() bool {
+	i.i++
+	return i.i <= i.l
+}
+
+// Key returns the key or index value of the current element.
+func (i *MapIterator) Key() Object {
+	k := i.k[i.i-1]
+
+	return &String{Value: k}
+}
+
+// Value returns the value of the current element.
+func (i *MapIterator) Value() Object {
+	k := i.k[i.i-1]
+
+	return i.v[k]
+}
diff --git a/vendor/github.com/d5/tengo/objects/object.go b/vendor/github.com/d5/tengo/objects/object.go
new file mode 100644
index 00000000..4c5aa7ae
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/object.go
@@ -0,0 +1,30 @@
+package objects
+
+import "github.com/d5/tengo/compiler/token"
+
+// Object represents an object in the VM.
+type Object interface {
+	// TypeName should return the name of the type.
+	TypeName() string
+
+	// String should return a string representation of the type's value.
+	String() string
+
+	// BinaryOp should return another object that is the result of
+	// a given binary operator and a right-hand side object.
+	// If BinaryOp returns an error, the VM will treat it as a run-time error.
+	BinaryOp(op token.Token, rhs Object) (Object, error)
+
+	// IsFalsy should return true if the value of the type
+	// should be considered as falsy.
+	IsFalsy() bool
+
+	// Equals should return true if the value of the type
+	// should be considered as equal to the value of another object.
+	Equals(another Object) bool
+
+	// Copy should return a copy of the type (and its value).
+	// Copy function will be used for copy() builtin function
+	// which is expected to deep-copy the values generally.
+	Copy() Object
+}
diff --git a/vendor/github.com/d5/tengo/objects/objects.go b/vendor/github.com/d5/tengo/objects/objects.go
new file mode 100644
index 00000000..f3878b11
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/objects.go
@@ -0,0 +1,12 @@
+package objects
+
+var (
+	// TrueValue represents a true value.
+	TrueValue Object = &Bool{value: true}
+
+	// FalseValue represents a false value.
+	FalseValue Object = &Bool{value: false}
+
+	// UndefinedValue represents an undefined value.
+	UndefinedValue Object = &Undefined{}
+)
diff --git a/vendor/github.com/d5/tengo/objects/return_value.go b/vendor/github.com/d5/tengo/objects/return_value.go
new file mode 100644
index 00000000..f7ef1dc4
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/return_value.go
@@ -0,0 +1,39 @@
+package objects
+
+import "github.com/d5/tengo/compiler/token"
+
+// ReturnValue represents a value that is being returned.
+type ReturnValue struct {
+	Value Object
+}
+
+// TypeName returns the name of the type.
+func (o *ReturnValue) TypeName() string {
+	return "return-value"
+}
+
+func (o *ReturnValue) String() string {
+	return "<return-value>"
+}
+
+// BinaryOp returns another object that is the result of
+// a given binary operator and a right-hand side object.
+func (o *ReturnValue) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *ReturnValue) Copy() Object {
+	return &ReturnValue{Value: o.Copy()}
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *ReturnValue) IsFalsy() bool {
+	return false
+}
+
+// Equals returns true if the value of the type
+// is equal to the value of another object.
+func (o *ReturnValue) Equals(x Object) bool {
+	return false
+}
diff --git a/vendor/github.com/d5/tengo/objects/string.go b/vendor/github.com/d5/tengo/objects/string.go
new file mode 100644
index 00000000..6a53b44d
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/string.go
@@ -0,0 +1,95 @@
+package objects
+
+import (
+	"strconv"
+
+	"github.com/d5/tengo/compiler/token"
+)
+
+// String represents a string value.
+type String struct {
+	Value   string
+	runeStr []rune
+}
+
+// TypeName returns the name of the type.
+func (o *String) TypeName() string {
+	return "string"
+}
+
+func (o *String) String() string {
+	return strconv.Quote(o.Value)
+}
+
+// BinaryOp returns another object that is the result of
+// a given binary operator and a right-hand side object.
+func (o *String) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	switch op {
+	case token.Add:
+		switch rhs := rhs.(type) {
+		case *String:
+			return &String{Value: o.Value + rhs.Value}, nil
+		default:
+			return &String{Value: o.Value + rhs.String()}, nil
+		}
+	}
+
+	return nil, ErrInvalidOperator
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *String) IsFalsy() bool {
+	return len(o.Value) == 0
+}
+
+// Copy returns a copy of the type.
+func (o *String) Copy() Object {
+	return &String{Value: o.Value}
+}
+
+// Equals returns true if the value of the type
+// is equal to the value of another object.
+func (o *String) Equals(x Object) bool {
+	t, ok := x.(*String)
+	if !ok {
+		return false
+	}
+
+	return o.Value == t.Value
+}
+
+// IndexGet returns a character at a given index.
+func (o *String) IndexGet(index Object) (res Object, err error) {
+	intIdx, ok := index.(*Int)
+	if !ok {
+		err = ErrInvalidIndexType
+		return
+	}
+
+	idxVal := int(intIdx.Value)
+
+	if o.runeStr == nil {
+		o.runeStr = []rune(o.Value)
+	}
+
+	if idxVal < 0 || idxVal >= len(o.runeStr) {
+		res = UndefinedValue
+		return
+	}
+
+	res = &Char{Value: o.runeStr[idxVal]}
+
+	return
+}
+
+// Iterate creates a string iterator.
+func (o *String) Iterate() Iterator {
+	if o.runeStr == nil {
+		o.runeStr = []rune(o.Value)
+	}
+
+	return &StringIterator{
+		v: o.runeStr,
+		l: len(o.runeStr),
+	}
+}
diff --git a/vendor/github.com/d5/tengo/objects/string_iterator.go b/vendor/github.com/d5/tengo/objects/string_iterator.go
new file mode 100644
index 00000000..8bc95eb5
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/string_iterator.go
@@ -0,0 +1,57 @@
+package objects
+
+import "github.com/d5/tengo/compiler/token"
+
+// StringIterator represents an iterator for a string.
+type StringIterator struct {
+	v []rune
+	i int
+	l int
+}
+
+// TypeName returns the name of the type.
+func (i *StringIterator) TypeName() string {
+	return "string-iterator"
+}
+
+func (i *StringIterator) String() string {
+	return "<string-iterator>"
+}
+
+// BinaryOp returns another object that is the result of
+// a given binary operator and a right-hand side object.
+func (i *StringIterator) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	return nil, ErrInvalidOperator
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (i *StringIterator) IsFalsy() bool {
+	return true
+}
+
+// Equals returns true if the value of the type
+// is equal to the value of another object.
+func (i *StringIterator) Equals(Object) bool {
+	return false
+}
+
+// Copy returns a copy of the type.
+func (i *StringIterator) Copy() Object {
+	return &StringIterator{v: i.v, i: i.i, l: i.l}
+}
+
+// Next returns true if there are more elements to iterate.
+func (i *StringIterator) Next() bool {
+	i.i++
+	return i.i <= i.l
+}
+
+// Key returns the key or index value of the current element.
+func (i *StringIterator) Key() Object {
+	return &Int{Value: int64(i.i - 1)}
+}
+
+// Value returns the value of the current element.
+func (i *StringIterator) Value() Object {
+	return &Char{Value: i.v[i.i-1]}
+}
diff --git a/vendor/github.com/d5/tengo/objects/time.go b/vendor/github.com/d5/tengo/objects/time.go
new file mode 100644
index 00000000..4e783cc8
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/time.go
@@ -0,0 +1,89 @@
+package objects
+
+import (
+	"time"
+
+	"github.com/d5/tengo/compiler/token"
+)
+
+// Time represents a time value.
+type Time struct {
+	Value time.Time
+}
+
+func (o *Time) String() string {
+	return o.Value.String()
+}
+
+// TypeName returns the name of the type.
+func (o *Time) TypeName() string {
+	return "time"
+}
+
+// BinaryOp returns another object that is the result of
+// a given binary operator and a right-hand side object.
+func (o *Time) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	switch rhs := rhs.(type) {
+	case *Int:
+		switch op {
+		case token.Add: // time + int => time
+			if rhs.Value == 0 {
+				return o, nil
+			}
+			return &Time{Value: o.Value.Add(time.Duration(rhs.Value))}, nil
+		case token.Sub: // time - int => time
+			if rhs.Value == 0 {
+				return o, nil
+			}
+			return &Time{Value: o.Value.Add(time.Duration(-rhs.Value))}, nil
+		}
+	case *Time:
+		switch op {
+		case token.Sub: // time - time => int (duration)
+			return &Int{Value: int64(o.Value.Sub(rhs.Value))}, nil
+		case token.Less: // time < time => bool
+			if o.Value.Before(rhs.Value) {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.Greater:
+			if o.Value.After(rhs.Value) {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.LessEq:
+			if o.Value.Equal(rhs.Value) || o.Value.Before(rhs.Value) {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.GreaterEq:
+			if o.Value.Equal(rhs.Value) || o.Value.After(rhs.Value) {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		}
+	}
+
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *Time) Copy() Object {
+	return &Time{Value: o.Value}
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *Time) IsFalsy() bool {
+	return o.Value.IsZero()
+}
+
+// Equals returns true if the value of the type
+// is equal to the value of another object.
+func (o *Time) Equals(x Object) bool {
+	t, ok := x.(*Time)
+	if !ok {
+		return false
+	}
+
+	return o.Value.Equal(t.Value)
+}
diff --git a/vendor/github.com/d5/tengo/objects/undefined.go b/vendor/github.com/d5/tengo/objects/undefined.go
new file mode 100644
index 00000000..79a380f5
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/undefined.go
@@ -0,0 +1,42 @@
+package objects
+
+import "github.com/d5/tengo/compiler/token"
+
+// Undefined represents an undefined value.
+type Undefined struct{}
+
+// TypeName returns the name of the type.
+func (o *Undefined) TypeName() string {
+	return "undefined"
+}
+
+func (o *Undefined) String() string {
+	return "<undefined>"
+}
+
+// BinaryOp returns another object that is the result of
+// a given binary operator and a right-hand side object.
+func (o *Undefined) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *Undefined) Copy() Object {
+	return o
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *Undefined) IsFalsy() bool {
+	return true
+}
+
+// Equals returns true if the value of the type
+// is equal to the value of another object.
+func (o *Undefined) Equals(x Object) bool {
+	return o == x
+}
+
+// IndexGet returns an element at a given index.
+func (o *Undefined) IndexGet(index Object) (Object, error) {
+	return UndefinedValue, nil
+}
diff --git a/vendor/github.com/d5/tengo/objects/user_function.go b/vendor/github.com/d5/tengo/objects/user_function.go
new file mode 100644
index 00000000..1d9bb4f7
--- /dev/null
+++ b/vendor/github.com/d5/tengo/objects/user_function.go
@@ -0,0 +1,47 @@
+package objects
+
+import (
+	"github.com/d5/tengo/compiler/token"
+)
+
+// UserFunction represents a user function.
+type UserFunction struct {
+	Name  string
+	Value CallableFunc
+}
+
+// TypeName returns the name of the type.
+func (o *UserFunction) TypeName() string {
+	return "user-function:" + o.Name
+}
+
+func (o *UserFunction) String() string {
+	return "<user-function>"
+}
+
+// BinaryOp returns another object that is the result of
+// a given binary operator and a right-hand side object.
+func (o *UserFunction) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *UserFunction) Copy() Object {
+	return &UserFunction{Value: o.Value}
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *UserFunction) IsFalsy() bool {
+	return false
+}
+
+// Equals returns true if the value of the type
+// is equal to the value of another object.
+func (o *UserFunction) Equals(x Object) bool {
+	return false
+}
+
+// Call invokes a user function.
+func (o *UserFunction) Call(args ...Object) (Object, error) {
+	return o.Value(args...)
+}